Incorrect work of the knee jerk indicates serious violations of the body. To diagnose the disease in the early stages, you should know what your reaction to a hammer blow under the knee says. Consider this in the article.
Reception of information from outside and its transmission throughout the body: through the muscles, organs, spinal cord and brain is ensured by the stable functioning of the nerves. The brain has a standard scheme for transmitting impulses along the way. In cases where an immediate response is required, the reflex travels through the spinal cord. Such a reaction occurs, for example, if you step on a needle, then the leg abruptly withdraws. If the reflex went through the brain, there would definitely be a delay in the process, which can be life-threatening for the organism.
The human knee jerk and its meaning. Arc knee jerk
So, a reflex is an instantaneous response to an external stimulus, it is coordinated by the nervous system. And its path is called a reflex arc. The signal of irritation is transmitted using afferent nerves to efferent centers in the spinal cord. Then hetransmitted to the muscles, which contract. The absence of reflexes is a symptom of a disease of the muscles, nervous system, brain, and a special emotional state. The vital processes of the body also work reflexively, such as the flow of saliva when eating food.
How to induce a knee jerk?
The occurrence of a knee jerk is due to the fact that during the impact of a medical hammer on the tendon of the quadriceps muscle, it contracts. This contraction causes the leg to straighten. The blow must be applied exactly under the patella, because the tendon of the extensor quadriceps muscle is fixed at the beginning of the tibia. It is not necessary to hit with force, the main thing is that the muscles are as relaxed as possible. You can throw one leg over the other, then when a patellar reflex occurs, it will twitch up.
What if other methods are needed?
If the traditional method does not work, there are several more methods for the manifestation of the knee jerk:
- The person should be seated on a chair so that the toes rest on the floor and the legs are bent at an angle of just over 90 degrees. The blow must be applied from top to bottom over the extended patella. As a result, the patella rises;
- the knee of the required leg should be placed over the second knee;
- you can use a high seat so that the legs hang down in a relaxed state;
- there is also a way when the patient is lowered ontoback with knees stacked one on top of the other.
There are times when the patient is physically unable to relax the examined limb sufficiently. Then the specialists apply methods of disinhibition of the knee reflex, for example, the techniques of Jendrassik and Shvetsov. Also, the patient should breathe deeply or solve simple mathematical problems aloud.
What do knee jerk disorders indicate?
Muscles contract in a similar way on the upper pair of limbs and elsewhere in the body. But the significance of the knee jerk is that its violation is considered an important symptom of abnormalities in the work of the brain and spinal cord. The arc of the knee jerk is constant. Only in rare cases, a he althy person may not have a knee jerk, while, most likely, a childhood illness has damaged his work. In the presence of diseases, it may be absent or, on the contrary, excessively intensified. This is due to the fact that the center of the knee jerk is located in the lumbar spinal cord, and more precisely in the II-IV segment. For some diseases, there are specific deviations in the manifestation of the knee jerk. For example, cerebral lesions cause a pendulum-like knee-jerk reflex. An enhanced reflex may indicate a form of neurosis. On the contrary, a reduced form of the reflex is a sign of infection or intoxication of the body. The complete absence of the knee jerk indicates a significant lesion of the nervous system. Also, the reflex may disappear inepileptics after a seizure, after using a tourniquet, during deep anesthesia or after heavy muscular exertion. Only a specialist can make an accurate diagnosis.
What is a reflex arc?
The knee jerk is due to its reflex arc. Just like a significant disruption in the overall working process of a mechanism due to the presence of a damaged part, the human body cannot function in the same way when something does not work correctly.. It is also called the neural arch. This name is explained by the fact that the knee jerk occurs due to impulses in the nerves that overcome a certain path. The reflex arc consists of chains of neurons that are formed from intercalary, receptor and effector neurons. They themselves and their offshoots create a pathway for the transmission of irritation.
What are the types of reflex arcs?
The peripheral nervous system has two types of reflex arcs:
- those that supply signals to internal organs;
- those related to skeletal muscles.
How does the knee-jerk reflex arc work?
The knee-jerk arc engages three sections of the back, from the second to the fourth. However, the fourth department is the most important in the process.
The reflex arc of the knee jerk has five components:
- Receptors. They receive the signal of the stimulus and are excited in response. These are the endsaxons or located in the cells of the epithelium of the body. Receptors are everywhere in the human body, in organs, in the skin, they make up the sense organs;
- Nerve fiber sensitive, afferent or centripetal. It transmits a signal to the center. Neuronal bodies are located outside the CNS, namely near the brain and in the nerve nodes near the spinal cord.
- Nerve center - the place where the signal is transmitted from the afferent neurons to the efferent. The centers of efferent neurons are located in the spinal cord.
- Nerve fiber is motor, centrifugal or efferent. As the name implies, excitation along it goes from the central nervous system to a specific organ. The efferent fiber is an axon (or a long process) of a centrifugal neuron.
- Effector. An organ that reacts to stimulation of a particular receptor. This is a muscle that contracts after processing a signal from the center, a gland that exudes juice due to nervous excitement, and more.
How does the knee jerk move?
For a detailed study of the knee jerk, you should study its stages. The passage of nerve impulses during the knee jerk occurs as follows:
- a blow with a hammer on the tendon under the knee causes this tendon to stretch, therefore, a receptor potential arises in the corresponding receptors;
- an action potential is born in the neural long process. In the spinal cord, it is chemically transferred to the motor neuron;
- the axon of an efferent neuron serves as a signal path tocalf muscle;
- due to muscle contraction, the leg twitches.
Now you know how the reflex works and for what purposes it is diagnosed.
